The present invention relates to a pressure transmitter and transmission method, and in particular to a pressure transmitter and transmission method suitable for measuring a fluid pressure or a pressure difference between two points in an atomic power plant, an oil refining plant, and a chemical plant and transmitting a detected signal.
The pressure/differential pressure transmitter transfers a fluid pressure received by a diaphragm to a sensor by using a sealed liquid sealed in a pressure guide path and transmits an electric signal detected by the sensor to the external. There are pressure transmitters that measure an absolute pressure and pressure transmitters that measure a differential pressure.
These pressure/differential pressure transmitters are used in atomic power plants, oil refining plants and the like. From the viewpoint of securing the safety of plants and product quality, for example, a precision of ±1% is demanded. However, it is difficult to keep the precision over a long term by influence of hydrogen transmitted from the outside of the pressure/differential pressure transmitter.
In other words, a part of hydrogen (hydrogen molecules, hydrogen atoms, and hydrogen ions) contained in a measurement fluid is transmitted by the diaphragm and then accumulated as air bubbles in a sealed liquid filled in a pressure guide path. As a result, the pressure within the pressure guide path rises and it becomes impossible to properly transmit a change of the pressure applied to the diaphragm to the sensor, resulting in a lowered precision.
Formerly, therefore, hydrogen transmitted through the diaphragm from the external is suppressed by providing an intermediate layer composed of any one or a plurality of aluminum, copper, platinum and gold that spreads nearly in parallel with the surface, within the diaphragm in a thickness direction as described in, for example, JP-A-9-113394, by making the diaphragm in a pressure receiving unit double and providing a gas trap having a sealed hydrogen absorption alloy in a gap between the double diaphragms as described in, for example, JP-A-2002-71494, or by providing a hydrogen absorption film on a sealed liquid side of a diaphragm in a pressure receiving unit.